Insects such as mosquitoes and ticks are not merely a nuisance, but can carry debilitating and sometimes fatal diseases that they infect their host with. Chemicals that repel these insects when placed on skin have been known for years with several of them also showing acceptably low levels of skin irritation and toxicity to mammals. Known repellents which possess these attributes include sec-butyl 2-(2-hydroxyethyl)piperidine-1-carboxylate, p-menthane-3,8-diol, ethyl N-butyl-N-acetyl-3-aminopropionate, and N,N-diethyl-meta-toluamide (referred to herein as “DEET”), with the latter being the most widely used.
Although a repellent such as DEET is not readily soluble in water, perspiration or exposure to water can decrease its concentration on skin, leading to formation of areas without adequate levels for repellency. Many patents disclose means of improving the water and sweat resistance of insect repellents by delivering them in a matrix of water-insoluble materials, particularly polymers that also provide abrasion and “rub-off” resistance. U.S. Pat. No. 3,590,118 discloses the use of a terpolymer of (meth)acrylic acid, ethyl or methyl methacrylate, and a C1 to C10 acrylate. U.S. Pat. No. 4,774,082 discloses the use of a copolymer of maleic anhydride and 1-alkene where from 10 to 40 mole percent of the polymer is a C18 to C30 1-alkene. U.S. Pat. No. 6,180,127 discloses the use of a copolymer of vinylpyrrolidone and a C4 to C30 1-alkene. U.S. Pat. No. 4,816,256 discloses the use of a terpolymer of isooctyl acrylate, stearyl methacrylate, and acrylic acid with a solubility parameter of 6 to 10 (cal/gm)1/2. Formulations containing these hydrophobic polymers are typically delivered from solutions containing high levels of lower alcohols such as ethanol or isopropanol that can cause irritation and drying of the skin.
Renewed focus has been placed on reduction of pollutants, particularly volatile organic compounds (referred to herein as “VOCs”) that create air pollution problems. The State of California has led the effort to reduce the emission of these VOCs from consumer products, limiting the percentage that can be included in products for sale. For non-aerosol insect repellents, the California Air Resources Board recently considered restricting the VOC content to 30% or less. The most straightforward and economical way to attain such a low VOC level in a cosmetically acceptable insect repellent is to use water as the major solvent. However, many of the repellents as well as the polymers used to impart splash and sweat resistance are not soluble in aqueous or hydroalcoholic solutions. Delivery as an emulsion with the polymer dissolved in the oil phase repellent is possible as disclosed in U.S. Pat. Nos. 6,605,643, 5,518,712, and 5,716,602. However, such two phase emulsions present problems with long term and freeze thaw stability, have prolonged dry times, may not wet and spread well on skin, and often include water-soluble surfactants that detract from their splash and sweat resistance and may irritate the skin.
A need thus exists for a low VOC/high water content topical insect repellent composition that is stable and single phase, non-irritating to the skin, spreads well and dries quickly, and contains a film-forming polymer that provides improved sweat and splash resistance on drying.